Immune complexes are present in the sera of rodents, primates and humans infected with malaria. These immune complexes inhibit phagocytosis and antibody dependent cell-mediated cytotoxicity. Because malarial antigens or peptides will eventually be used in a malarial vaccine, we propose to determine whether several rodent, primate and human antigens and antigen-antibody complexes are present in infected hosts. These antigens are of interest because they are putative protective antigens, some are present on the erythrocyte surface, and some have repetitive epitopes. The antigens and immune complexes will be detected by radioimmunoassay using specific monoclonal antibodies. One antigen, Pc100, located on the surface of Plasmodium chabaudi-infected erythrocytes will be purified and incorporated into immune complexes made with monoclonal antibodies. These complexes will be injected into mice and their effect on the course of malaria infection and on the mice will be determined. Since Pc100 is a model of an erythrocyte surface antigen which may be protective, it will be characterized biochemically. Further, the ability of monoclonal antibodies against Pc100 and purified Pc100 to protect mice against lethal and non-lethal P. chabaudi will be studied.